1. Field of the Invention
The present invention relates to an address search method for use in a disk player system.
2. Description of Background Information
Often players for playing an information recording disk (simply referred to as disk hereinafter) such as a video disk or a digital audio disk are provided with an address search function by which an address designated by an operator is searched in a short period of time.
Conventionally, the search operation has been performed in such a manner that an address difference between a present address on the disk at which an information reading light spot is located and a target address designated by the operator is computed, and the information reading spot is moved near to the target address by moving a slider carrying a pickup on the basis of the address difference obtained by the computation, and subsequently a jump pulse which is generated at predetermined intervals is supplied to a tracking actuator, so that a track jump operation through which the information reading light spot jumps over a predetermined number of recording tracks is repeated while performing a comparison between the present address and the target address.
The computation between the present address and the target address is performed by using a microcomputer and the like. However, with the conventional search method as described above, the computation is performed when the address difference is large, so that a lengthy computation program is required.
On the other hand, for this search operation, as mentioned above, it is indispensable to employ the so-called track jump operation by which the information reading spot for reading information on the disc is moved to jump a recording track or recording tracks on the disk. In order to perform the track jump operation, a jump pulse is supplied to a tracking actuator provided for displacing the information reading spot in a direction of disc radius. The application of a jump pulse in the form of a voltage or a current to the tracking actuator means that a corresponding kinetic force is applied to a moving part of the tracking actuator. If a constant kinetic force is applied, a frequency characteristic of the response in distance will become as illustrated in FIG. 1. Therefore, if the frequency of generation of the jump pulse is sufficiently higher than the low frequency resonance frequency f.sub.0, the distance of shift by the tracking actuator will have a value corresponding to the double integral of the jump pulse
This point will be described specifically with reference to FIGS. 2A through 2D. When a jump pulse (a) as shown in FIG. 2A arrives, the pickup is accelerated at an acceleration factor a during a period from t.sub.0 to t.sub.1 as illustrated in FIG. 2B. Therefore, the speed v of movement of the pickup increases gradually, and reaches a value at.sub.1 (v=at.sub.1) at the time t.sub.1 (t=t.sub.1), as illustrated in FIG. 2B. The pickup is then decelerated by the application of a voltage having the opposite polarity at the time t.sub.1, and the speed of movement reaches zero at a time 2t.sub.1 (t=2t.sub.1). The distance traveled by the pickup is equal to at.sub.1 /2 during the acceleration range, and equal to at.sub.1 /2 during the deceleration range, and the total distance of shift (d) is equal to at.sub.1, as illustrated in FIG. 2D. If the pulse width of the jump pulse (a) is determined so that the above mentioned total distance of shift (d) is equal to the track pitch, the pickup is moved from a recording track to an adjacent track by the application of one jump pulse, and the number of recording tracks over which the pickup is moved by the jump operation is determined by the pulse width of the jump pulse (a).
On the other hand, if a jump pulse having a large pulse width is applied for jumping a large number of recording tracks. e.g., one hundred of recording tracks at one time, the frequency of generation of the jump pulse approaches to the resonance frequency f.sub.0 of the actuator, and the response of the pickup will become as illustrated in FIGS. 3A through 3D. As shown in FIG. 3C, the pulse width of the deceleration pulse becomes excessive with respect to the pulse width of the acceleration pulse, and the pickup will be moved back after once reaching to a maximum travel distance, as shown in FIG. 3D.
Therefore, it is necessary to precisely control the pulse width of the deceleration pulse with respect to the acceleration pulse However, the control of the pulse width of the deceleration pulse is not easily performed, and the number of tracks across which the pickup is moved by one track jump operation is limited.